Electromagnetic pumps have been known for several years in which the molten metal entering the pumping conduit by "metallostatic" pressure is moved by a force resulting from the combined action of a magnetic field created in a slice of molten metal and of an electric current flowing across the said slice of molten metal perpendicularly to the direction of the magnetic field. Electromagnetic pumps of this type comprise a first magnetic circuit provided with a first gap through which the pumping conduit passes and a second magnetic circuit which induces the current in an electric circuit passing through the said slice of molten metal.
It appears to be particularly advantageous to induce the said electric current in a conductive turn threaded by the second magnetic circuit. It is known that such a conductive turn can be advantageously constituted by a hollow ring filled with molten metal by "metallostatic" pressure when the pump is immersed in a ladle containing molten metal to be pumped. Finally the pump is made immersable by potting its active parts in a block of ceramic material appropriately resistent to all corrosive action of the molten metal and to repeated thermal shocks to which the pump will be subject each time it is put into service and each time it is stopped.
The turn is generally horizontal and closed. It is connected to the pumping conduit at the level of the gap in the first magnetic circuit by two tips or by two electrodes and in such a way that the molten metal flows only in the pumping conduit. In contrast the molten metal stays substantially motionless in the turn while the pump is immersed and in operation.
Experience has shown that when the molten metal contains impurities or dispersed slag, the conductive turn becomes furred after being in operation for some time and that finally it becomes at least partially obstructed which reduces the performance of the pump.
Another type of immersible pump is also known and comprises essentially a magnetic circuit having three vertical columns. The central column includes a gap. The conduit passes through the central column and is horizontally disposed in the gap and adjacent thereto. This conduit has one end in molten metal. The other end is connected to a pumping pipe which is inclined to the horizontal. The molten metal enters the gap by "metallostatic" pressure in the conduit when the pump is immersed and is subjected to the action of the vertical magnetic field formed in the gap of the central column of the magnetic circuit.
Further the conduit is threaded by the magnetic circuit formed by the other two vertical columns. A current is thus induced in the conduit and the loop is closed through the molten metal. Under the combined action of the induced horizontal current and the vertical magnetic field, there appears a force perpendicular to both the induced current and to the vertical magnetic field. This force acts on the slice of molten metal which is contained in the gap and which is thus horizontal. The molten metal is pressurized by this force and it is the indirect action of the pressure which causes the molten metal to rise in the inclined pumping conduit.
This results in the efficiency of a pump of the second pump being fairly low. Further the point where the pumping pipe begins its inclination constitutes an angle where impurities have a tendancy to accumulate without it being very easy to remove them.
Thus to pump metal which includes impurities it has appeared advantageous to use a magnetic circuit structure which is fairly close to induction pumps of the first type combined with a conductive circuit which is open at both its ends in the molten metal and which is closed electrically through the mass of molten metals. By virtue of its accessibility via its ends, this conduit will be very easy to clean in the event of an accumulation of impurities. Further it will be possible to subject the slice of molten metal to a vertical force resulting from the combination of a horizontal induced current and a horizontal magnetic field in the gap of the first magnetic circuit.
Since the conductive circuit is open at both its ends the induced current is closed through the bath of molten metal. It is easy to see that the cross-section of the equivalent turn is thus increased, thereby reducing its resistance in view of the good electrical conductivity of a bath of molten metal.
Further since the turn thus formed remains in permanent contact with the molten metal while the pump is immersed, it is possible to feed the pump by means of this horizontal conduit.